An x-ray tube may include a vacuum housing having at least one cathode and at least one anode disposed therein. The at least one cathode and the at least one anode may be insulated by at least one insulation element. The cathode (e.g., a flat panel emitter, a filament) emits electrons that strike the anode as an electron beam when a high voltage is applied to the cathode.
The electron beam is accelerated towards the anode and strikes the surface of the anode, thereby creating x-ray radiation in the anode material. The x-ray radiation exits as useful x-ray radiation from an x-ray beam exit window in the vacuum housing. The x-ray radiation may be used for imaging processes in the medical or non-medical fields.
With rotating anodes (e.g., rotating anode x-ray tubes or rotating envelope x-ray tubes), compensation may be made for rotation of the anode. The compensation is achieved using deflection electrodes. The electron beam may be focused even in small spaces using deflection electrodes that are arranged close to the cathode (e.g., on the focus head). The deflection electrodes may apply and maintain variable deflection voltages to the cathode voltage. The deflection electrodes may be insulated from the cathode (e.g., insulated from the focus head). The insulation elements may be glass or ceramic passthroughs. The insulation elements may have a reference to the cathode voltage (e.g., HV potential of the cathode).
Because of the space available in the area of the cathode, the size of the insulation elements may be configured for only normal operation although this is not problematic.
A drop in potential that affects the cathode may occur in the event of a technically unavoidable “arcing.” The term “arcing” refers to voltage flashovers and voltage discharges (e.g., exceeding tolerance range of the rated voltage) that occur as transient events (e.g., at random and, therefore, unpredictable times).
Temporally resolved, the potential of at least one of the deflection electrodes and/or the potential of the focus head is reduced by the above-described drop in potential. The deflection electrodes disposed as insulated electrodes briefly remain at full potential. The deflection voltage may also be present at the deflection electrodes.
Since the high-voltage is not generated directly at the cathode, a delay may occur while the focus head and the deflection electrodes adapt to the same potential. During the interim, almost all of the voltage drops across the insulation elements of the deflection electrodes. Further discharges may result shortly after the arcing and may lead to an accelerated destruction of the sensitive insulation elements of the deflection electrodes. Due to the energy-rich discharge, discharge traces on the insulation elements and material deposits on the insulation elements may occur. The material deposits are detrimental to the vacuum in the vacuum housing and, therefore, to operation of the x-ray tube.